Devices operated wirelessly have been used for a long time. Batteries may power such devices. However, batteries have limited capacity and lifetime. In order for the batteries to last long, the devices are designed for as small power consumption as possible.
An article surveillance system uses several identification tags attached to the articles of the system. Readers are arranged to detect the presence and identity of such tags within the coverage area of the reader.
An intrusion alarm system uses several sensors arranged to detect unauthorized persons adjacent the sensor. A central system is alerted if a sensor is trigged.
A temperature monitoring system of a building comprises several temperature sensors arranged to detect the temperature adjacent the sensor. A central computer polls the sensors intermittently for receiving temperature values. The sensors may as well detect humidity and other data, such as mains power consumption or light conditions (night or day light).
Such systems have in common that a plurality of battery-powered devices are included in the system. The devices may be operated intermittently or continuously for delivering data to a central system. Other systems than those described above may also benefit from the present invention.
The device may be “sleeping” for a long time, such as in article surveillance systems, wherein an identification tag is attached to an article during manufacture and may reside on the article during transport and storage during months and years, until used by the system at the time of selling the article.
Thus, there is a need for a battery-powered device having a very low power drain during a “sleep” mode and which can be activated at an arbitrary time by a predetermined signal. Moreover, there is a need for a device having an identity and possibly data that can be detected by a remote system.
WO 01/67625 discloses a transponder for amplification of a received signal to a signal for retransmission, wherein a quenched oscillator is incorporated as an amplifying element. The oscillator is preferably of the superregenerative type and exhibits negative resistance for the received signal.
WO 96/08086 discloses a micropower transponder that employs a superregenerative receiver wherein the quench oscillator is external to the regenerative transistor. The quench oscillator applies en exponentially decaying waveform rather than the usual sinewave to achieve high sensitivity at microampere current levels.